1. Field of the Invention
This invention relates to a carburetor assembly comprising a rich set carburetor for supplying rich fuel-air mixtures and a lean set carburetor for supplying lean fuel-air mixtures and adapted for use with an internal combustion engine of the so-called stratified charge combustion type wherein a rich mixture section and a lean mixture section are formed in a combustion chamber, and wherein a flame of combustion produced by igniting the rich fuel-air mixture in the rich mixture section is used to ignite and burn the lean fuel-air mixture in the lean mixture section.
2. Description of the Prior Art
Generally, internal combustion engines of the startified charge combustion type are capable of reducing the amounts of oxides of nitrogen, carbon monoxide and hydrocarbons in the exhaust gases by increasing the leanness of the fuel-air mixture drawn by suction into the engine as a whole. One example of this type of engine which has been proposed is an internal combustion engine of the torch ignition type comprising a main combustion chamber section receiving a supply of lean fuel-air mixtures, and an auxiliary combustion chamber section maintained in communication with the main combustion chamber section through a torch opening and adapted to receive a supply of rich fuel-air mixtures. In an internal combustion engine of the torch ignition type, a flame of combustion produced in the auxiliary combustion chamber section is ejected through the torch opening into the main combustion chamber section so as to ignite and burn the lean fuel-air mixture in the main combustion chamber section.
The internal combustion engine of the torch ignition type constructed as aforesaid is provided with a rich set carburetor for supplying rich fuel-air mixtures to the auxiliary combustion chamber section, and a lean set carburetor having a primary side carburator and a secondary side carburetor for supplying lean fuel-air mixtures to the main combustion chamber section. Preferably, they are formed integrally with each other and receive a supply of fuel from a single float chamber. This is because the arrangement enables minimization of the problems which might be raised in connection with the layout of the engine and the accumulated errors of links and the like which determine the relative positions of the rich and lean set carburetors. Also, it is in order to reduce the number of component parts and simplify the construction of the carburetor assembly as a whole that a single float chamber is shared by the two carburetors. One of the problems raised in designing such carburetor assembly is how to cope with variations in the inclination of a fuel surface in the float chamber.
Generally, it is known that the types and amounts of noxious components of the exhaust emission of an internal combustion engine of the torch type depend on the performance of the main combustion chamber of the torch ignition type. More, specifically, since the main combustion chamber section has a volume which is much greater than the volume of the auxiliary combustion chamber section, the flow of fuel to the main combustion chamber section per one cycle is much greater in volume than the flow of fuel to the auxiliary combustion chamber section, no matter how thin the fuel-air mixture supplied to the main combustion chamber section may be. This makes it necessary to effect control, with a high degree of precision, of the ratio of the two flows to be mixed with each other (volume of air/volume of fuel). In an engine mounted on a motor vehicle, the fuel surface in the float chamber of the carburetor will be inclined due to the fact that the motor vehicle must take a short turn or accelerate or decelerate suddenly in view of the purposes it is intended to serve. This will cause variations in the air-fuel ratio of the mixtures supplied to the engine. It will thus be appreciated that it is essential to arrange the float chamber substantially in the vicinity of the center of the lean set carburetor so as to thereby minimize the influences of the tilting of the motor vehicle.
However, this arrangement is not without a disadvantage. That is, when the motor vehicle takes a short turn or decelerates or accelerates suddenly, the fuel-air mixture supplied to the rich set carburetor will be influenced by inclination of the fuel level in the float chamber and its richness will be increased. If this phenomenon occurs, the ignition plug disposed in the auxiliary combustion chamber section will get wet and become unable to produce a flame in the auxiliary combustion chamber section. As a result, the fuel-air mixture in the main combustion chamber section will not burn, thereby causing an increase in the amounts of noxious components of the exhaust gases, particularly those of hydrocarbons. This is not desirable from the point of view of controlling exhaust emissions of motor vehicles.
Another solution of the problem of how to eliminate the influences of the inclined fuel level that comes to mind would be to arrange main nozzles of the lean and rich set carburetors at positions which are at a higher level than the positions in which they have hitherto been disposed (if this is the case, the float chamber may be disposed in any position as desired). However, this arrangement would cause the trouble of the fuel flow lagging behind the air flow and would make it impossible to supply the engine with mixtures of the proportions of fuel and air which meet the requirements of the engine. More specifically, if the air bleed and the fuel jet of the prior art are employed without any alteration, there will be a delay in the fuel flow which corresponds to the increase in the height of the main nozzles. If the design of the air bleed, the fuel jet and the diameter of the Venturi were altered to eliminate the delay in the fuel flow, the air-fuel ratios of the mixtures and the volumes of air supplied to the engine would be unable to meet the requirements of the engine. Particularly, unless the mixture supplied to the main combustion chamber is controlled with a high degree of precision as aforementioned, it will be difficult to effect exhaust emission control satisfactorily.